1. Field of the Invention
The present invention relates to a system for controlling slip generated at the drive wheels of a vehicle upon an acceleration thereof by controlling an output torque of an internal combustion engine.
2. Description of the Related Art
Various systems capable of controlling slip generated at the drive wheels of a vehicle upon acceleration, by controlling an output torque of an internal combustion engine, are known, and in one such system for reducing an output torque of an internal combustion engine, for example, a number of cylinders at which a fuel cut is carried out is varied in accordance with the degree of slip of the drive wheels during acceleration (see Japanese Unexamined Patent Publication No. 58-8436). Also, a system is known in which the ignition timing is delayed with respect to the optimum timing when acceleration slippage occurs (see Japanese Unexamined Patent Publication No. 62-67257).
Nevertheless, in addition to the system for controlling acceleration slippage, an automobile is usually provided with various control devices for controlling the engine in accordance with engine operating conditions, to obtain a high engine output and reduce vibration, etc., in the vehicle. Among these systems is a knocking control system provided for obtaining an effective output torque of an internal combustion engine, where an ignition timing is retarded with respect to the optimum timing upon detection of an occurrence of knocking, and is advanced with respect to the delayed timing when knocking is not detected, to thereby obtain an effective output power from the engine without the generation of knocking.
These slip and knocking controls of the prior art are carried out independently in line with respective requirements, an therefore, the following difficulty arises. When a knocking control is carried out, and simultaneously acceleration slippage is generated in the drive wheels due to a depression of an accelerator pedal by a driver, a control of the engine output torque as required by the knocking control system and a control of an engine output torque as required by the slip control system occur simultaneously and often are contradictory. Accordingly, a situation can arise wherein the slip control system operates to reduce the engine output torque, while the ignition control system operates to increase the engine output, which causes the control of the slippage to be worsened, i.e., a desired acceleration of the vehicle cannot be obtained because the slippage is not controlled. For example, where the control of the engine output torque is carried out by using a fuel cut operation at a specific cylinder(s), a retarding of the ignition timing or a closing of a subthrottle valve, or a change in the selected number of cylinders, the degree of retarding of the ignition timing or degree of opening of the throttle valve as calculated in accordance with the degree of slippage of the drive wheels is influenced and varied by the control of the ignition timing for controlling the knocking, which obviates an effective control of the slippage of the drive wheels.
Furthermore, vibration occurs in the engine under the fuel cut operation for lowering the engine output, and thus the knocking control system is sometimes erroneously operated. As a result, the delay control for suppressing the knocking and the delay control for suppressing the acceleration are combined, and thus the engine is operated under an extremely retarded ignition timing, which causes the engine output to be greatly reduced and lowers the acceleration performance.